Onion Architecture in Development

I have already written a detailed article on MediatR and CQRS patterns in ASP.NET Core 3.1 WebApi Project. We will have to register Swager within the application service container. Navigate to ../Startup.cs and add these lines to the ConfigureServices method. To keep things simple but demonstrate the architecture to the fullest, we will build an ASP.NET Core Web API that is quite scalable.

Advantages of onion architecture

To keep things clean, what we can do is, Create a DependencyInjection static Class for every layer of the solution and only add the corresponding. It represents the Domain Entities layer of the onion architecture. The layer https://globalcloudteam.com/ is intended to create an abstraction layer between the Domain entities layer and the Business Logic layer of an application. It is a data access pattern that prompts a more loosely coupled approach to data access.

Value objects

Resident Workflow Action and Non-Resident Workflow Actions . Engine will then run the business logic and will communicate with OData. BusinessAPIs will be proprietary APIs and access to these APIs will be subscription based . This approach makes it possible to create a universal business logic that is not tied to anything.

UI – User interface will be MVC based and will only interact with Business APIs and will only responsible for displaying the data and sending the data back to BusinessAPIs. The Infrastructure Layer should not implement any business logic, as well as any use case flow. DTOs are well suited as objects with really specific formats and data. Your Domain models can have Value objects in their attributes, but the opposite is not allowed. The popularity of microservices is growing due to the range of benefits they offer to developers and businesses.

We now know that Onion Architecture has a significant role in implementing a domain-driven design. Great job with the architecture and thanks for sharing. Well, you are in luck 😛 I already have a complete implementation of Blazor Clean Architecture. The best way would be to rely on Repository layers that can create the necessary abstraction over the Data Access Technology. You can now move the EFCore to an Infrastructure Layer. Yes, As a matter of fact I am already building a Solution for Clean Architecture in ASP.NET Core 3.1 WebApi.

As mentioned earlier, the Core Layers will never depend on any other layer. Therefore what we do is that we create interfaces in the Application Layer and these interfaces get implemented in the external layers. This is also known and DIP or Dependency Inversion Principle. We started at the domain level, where we looked at our entity definitions and repository interfaces and exceptions. ContractsProject to define the data transfer objects that we will use with the service interfaces. We have already prepared a working project for you and we will look at each of the projects in the solution and talk about how they fit into the onion architecture.

Anemic Domain Models

At least this approach could be achieved by using relaxed layering. After Adding the DbSet properties we need to add the migration using the package manager console and run the command Add-Migration. It provides us with better testability for unit tests, we can write the separate test cases in layers without affecting the other module in the application. Onion architecture uses the concept of the layer but is different from N-layer architecture and 3-Tier architecture. We could create an initialization script, connect to the Docker container while it is running the database server, and execute the script. But this is a lot of manual work, and it is error-prone.

  • Next, we looked at the Infrastructure layer, where the implementations of the repository interfaces are placed, as well as the EF database context.
  • The UserController has an action method named DeleteUser, which returns view to delete a user.
  • Stored procedures because we find the easy maintenance and also easy to write the logic.
  • On the other hand, Onion Architecture addresses both the separation of concern and tight coupling issues.
  • The obvious benefit of the onion architecture is that our controller methods become very lightweight.

We will add the interfaces that consist the of data access pattern for reading and writing operations with the database. We will add the interfaces that consist of the data access pattern for reading and writing operations with the database. These interfaces communicate between UI and data access logic. As it communicates via interfaces, it builds applications that are loosely coupled. This project represents the Service layer of the onion architecture. This layer is used to communicate with the presentation and repository layer.

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The domain layer is the innermost layer of the architecture. Both software developers and domain experts should be able to talk in a Ubiquitous Language. It’s a software that any developer should be able to do improvements and fixes without worrying about breaking something under the hood. Any developer, familiar with the domain, should be able to understand the code, and easily know where to change things.

Advantages of onion architecture

Few of the solutions developed and maintained by Microsoft MVPs like eShopOnWeb and eShopOnContainers also follow a similar . I have written a detailed article on API Versioning in ASP.NET Core 3.1 WebApi. Feel feel to read it to get a complete idea of this concept. Now add a Product Class that inherits the Id from the BaseEntity. Create a new class Entities/Product.cs in the Domain Project. To do this, right-click the WebApi Project and go to properties.


The circles symbolize distinct levels of responsibility. The deeper we go, the more we know about the domain and business rules. The outer rings are mechanisms , whereas the inside circles are fundamental domain logic. The outer layers rely on the inner layers, and the inner layers are unaffected by any changes being introduced in the outer rings. Jeffrey Palermo coined the term “Onion Architecture” in 2008. This architecture enables greater application testability, maintainability, and dependability on infrastructures such as databases and services.

This article introduced Onion Architecture in ASP.NET Core, using Entity Framework Core with the “code first” development approach. We used Bootstrap, CSS, and JavaScript for the user interface design in this application. We create one more interface named IUserProfileService. This interface holds method signature which is accessed by the external layer for the UserProfile entity.

After adding all the layers our project structure will look like this. The Domain Interfaces onion architecture are implemented in the Supermarket.Core project. Since a Domain Interface acts on an Entity, it should be considered pure business logic. Using dependency inversion throughout the project, depending on abstractions and not the implementations, allows us to switch out the implementation at runtime transparently. We are depending on abstractions at compile-time, which gives us strict contracts to work with, and we are being provided with the implementation at runtime.

The domain models and services will be inside this layer, containing all the business rules of the software. It should be purely logical, not performing any IO operations at all. Onion Architecture is based on the inversion of control principle.

Even in the application layer, there is obviously no one approach to avoiding this this hell completely. Another approach to look at the problems described above is to look at the Traditional Architecture diagram below. It should only return Domain Models without actually exposing the implementation of onion architecture how this is done. We can then implement the repository interfaces in various ways and we can even switch amongst implementations at run time using dependency injection and inversion of control. On the other hand, the Onion Architecture tackles the problems of tight coupling and separation of concerns.

Why Microservices Are Good for Our Project

This will be an Empty API Controller which will have Api Versioning enabled in the Attribute and also a MediatR object. We will not have to re-define the API Versioning route nor the Mediatr object. When there is just a logical separation in your application, we can term it as layers or N Layers. In cases where there is both a physical and logical separation of concerns, it is often referred to as n-tiered application where n is the number of separations. In this article, we will deal with the Layered Architecture.

Language and framework independent

Database Independent – Since we have a clean separation of data access, it is quite easy to switch between different database providers. You can see the clear separation of concerns as we have read earlier. The GET request for the DeleteUser action method returns _DeleteUser partial View. The code snippet mentioned below is under the User folder of Views.

These days we have a different idea of what should go in a layer than 30 years ago, and we are more careful about where we put domain logic, presentation logic, and so on. But the architectural principles are all essentially the same. This is a infrastructure concern and should be handled by the application infrastructure.

Repositories, external APIs, Event listeners, and all other code that deal with IO in some way should be implemented in this layer. For example, let’s say you are developing a banking system. Then, you are implementing a use case which lets the user check her or his account balance.

It can be a separate repo that creates external resources or a tool that lives in the application’s repo but runs before the application itself. Still not completely clear about what goes where but your article has greatly improved my understanding about this architecture. I also liked that you started with a clean slate as most out there just show it ready-made and try to explain from there. I am leaning towards the API template as I usually use SPA’s. That’s quite everything in this simple yet powerful implementation of Onion Architecture in ASP.NET Core.

How to Migrate On-premise SQL Database to Azure

This file holds all the configuration required for the app launch. Thus, swagger will open up by default every time you run the application. The Onion architecture, introduced by Jeffrey Palermo, overcomes the issues of the layered architecture with great ease. With Onion Architecture, the game-changer is that the Domain Layer is at the Core of the Entire Application. In this approach, we can see that all the Layers are dependent only on the Core Layers.

Then, run the following commands to add migrations and to generate / update the database. We could create a startup script, connect to the Docker container while the database server is running, and run the script. Composition of the Dockerto bundle our web application container with a container running the PostgreSQL database image. This way we don’t have to have PostgreSQL installed on our system. Presentationproject and configure them with the framework. They are treated the same as if they were conventionally defined.

The inner layers shouldn’t know if your application is being exposed through an API, through a CLI, or whatever. This layer is also allowed to know about everything contained in the inner layers, being able to import entities from the Application and Domain layers. Example of a simple business ruleSo, for these given examples, if computers did not exist, the Business rules would still be applied. This rule of thumb usually can help you distinguish between these different kinds of rules. As this layer is purely logical, it should be pretty easy to test it, as you don’t have to worry about mocking IO operations.

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